Fix arg k, m to be required

Right now ECDriver doesn't check if k, m exist in the kwargs for init.
That can tigger unfortunately success to init and that will fail at
encode/decode (or result in odd with get_segment_info)

Once, we have jerasure_rs_vand in default, that worked becuase jerasure
did the assertion for the k, m parameters but we can reproduce the
failures which this patch want fix with like:

driver = ECDriver(ec_type='liberasurecode_rs_vand')   # <- this is
default and it succeeded!
driver.encode(' ')  # <- And then, this will result in ECDriverError:
Out of memory, whooa!

This patch fixes this to check the k, m existence in the init process.

Change-Id: I0757c0a4e510ba42f357db0cac22861919d0ca26

pyeclib/ec_iface.py

@@ -114,6 +114,12 @@ class ECDriver(object):
         self.ec_type = None
         self.chksum_type = None
         self.validate = False
+
+        for required in ('k', 'm'):
+            if required not in kwargs:
+                raise ECDriverError(
+                    "Invalid Argument: %s is required" % required)
+
         for (key, value) in kwargs.items():
             if key == "k":
                 try:

test/test_pyeclib_api.py

@@ -109,6 +109,34 @@ class TestPyECLibDriver(unittest.TestCase):
     def tearDown(self):
         pass
 
+    def test_invalid_km_args(self):
+        for ec_type in VALID_EC_TYPES:
+            # missing k
+            with self.assertRaises(ECDriverError) as err_context:
+                ECDriver(ec_type=ec_type, m=1)
+
+            self.assertEqual(str(err_context.exception),
+                             "Invalid Argument: k is required")
+
+            # missing m
+            with self.assertRaises(ECDriverError) as err_context:
+                ECDriver(ec_type=ec_type, k=1)
+
+            self.assertEqual(str(err_context.exception),
+                             "Invalid Argument: m is required")
+
+            with self.assertRaises(ECDriverError) as err_context:
+                # m is smaller than 1
+                ECDriver(ec_type=ec_type, k=-100, m=1)
+            self.assertEqual(str(err_context.exception),
+                             "Invalid number of data fragments (k)")
+
+            with self.assertRaises(ECDriverError) as err_context:
+                # m is smaller than 1
+                ECDriver(ec_type=ec_type, k=1, m=-100)
+            self.assertEqual(str(err_context.exception),
+                             "Invalid number of data fragments (m)")
+
     def test_valid_ec_types(self):
         # Build list of available types and compare to VALID_EC_TYPES
         available_ec_types = []